1. Field of the Invention
The present invention relates to a roller cage made of metal for holding a roller of a roller bearing and, more particularly, relates to the technique for, at the time of press-molding a contact surface contacting to the rolling surface of the roller at the peripheral portion of a window hole for receiving the roller, performing the press-molding so as not to degrade the accuracy of the size of the roller cage.
2. Description of the Related Art
Conventionally, various types of roller bearings have been employed, and some of them employ a roller cage which is formed by press-molding a metal plate of steel plate or the like.
An example of such a roller cage made of metal will be explained with reference to FIG. 11. A roller cage 1 includes a plurality of window holes 2 for receiving a plurality of rollers respectively, a pair of front and rear flange portions 3, 4 for sandwiching the window holes 2 along the direction of the rotational axis of the roller bearing, and a plurality of separation bars 5 for separating the window holes along the rotational direction of the roller bearing. The roller cage 1 serves to hold a plurality of rollers 8, which roll while being in contact with an inner ring 6 and an outer ring 7 of the roller bearing, along the rotational direction of the roller bearing with a constant interval thereamong, as shown in FIG. 12.
As shown in FIG. 12, each of the separation bars 5 is provided with contact surfaces 9 contacting with the rolling surfaces of the adjacent rollers 8 at the peripheral portions of the adjacent window holes on the upper surface 5a side of the each separation 5 bar 5. Each of the contact surfaces 9 is formed as schematically shown in FIG. 13 in a manner that the side surfaces 10, which are formed at the time of forming the corresponding one of window holes 2 by the stamp-molding process, are subjected to the press-molding by using a pressing die 11 and a backing (supporting) die 12 to press to the vertical direction in the figure thereby to form the contact surfaces. Accordingly, since the contact surfaces 9 can be made smooth, such a problem can be surely prevented that the abrasion is caused on the rolling surface of the roller 8.
At the time of subjecting the contact surfaces 9 of the roller cage 1 to the press-molding, the roller cage is pressed from a direction perpendicular to the axial direction thereof regardless of the type of the roller cage. When the pressing die 11 presses the upper surface side peripheral portions 10a of the window holes 2, portions (sectional areas) shown by a symbol S0 in FIG. 13 are 20 pressed and simultaneously portions (sectional areas) shown by symbols S1 and S2 in FIG. 13 expand.
However, in the related press-molding method for the roller cage 1, since the backing die 12 supports the entirety of the lower surface 5b of the separation bar 5, the separation bar 5 can not 25 be freely deformed at the time of the press-molding.
Thus, since the sum (S1+S2) of the increments of the sectional areas of the separation bar 5 is smaller than the decrement (S0) of the sectional area thereof, the separation bar 5 extends to an elongated direction of the separation bar in order to compensate the decrease of the sectional area. As a result, the accuracy of the size of the roller bearing degrades.
Thus, in the related art, in order to reduce the amount of the expansion of the separation bar 5 caused at the time of press-molding the contact surface 9, there have been employed such a method that the stroke of the pressing die 11 is reduced thereby to make the area of the contact surface 9 narrower, or that the size of the separation bar is set in view of the expansion of the separation bar 5. However, in each of such related methods, the number of required press-molding processes becomes quite large.
Further, in the related art, since it is difficult to manage the accuracy of the size of the roller cage, there has been a demand for the press-molding technique which can process a roller cage without degrading the accuracy of the size thereof.
In view of the above, an object of the present invention is to eliminate the aforesaid problems of the related art and to provide a roller cage which, at the time of press-molding a contact surface contacting to the rolling surface of a roller at the peripheral portion of a window hole for receiving the roller, can perform the press-molding so as not to degrade the accuracy of the size of the roller cage.
The aforesaid object of the present invention can be attained by the following roller cage made of metal for holding rollers of a roller bearing. The roller cage includes: separation bars separately defining a plurality of window holes along a peripheral direction of the bearing with a constant interval thereamong. The window holes respectively receive said rollers therein. Each of the separation bars includes: a contact surface being formed by press-molding one of an outer diameter surface side end portion and an inner diameter surface side end portion thereof, and contacting with the rolling surface of the roller; and an expansion portion expanding to a radial direction of the bearing at the other of the outer diameter surface side end portion and the inner diameter surface side end portion which is not subjected to the press-molding.
That is, according to the present invention, at the time of press-molding the contact surface contacting with the roller at the upper surface side peripheral portion of each of the window holes of the roller cage, one of the outer diameter surface side end portion and the inner diameter surface side end portion which is not subjected to the press-molding can be freely deformed to the pressing direction without being restricted by a backing die.
Accordingly, since the increase and the decrease of the sectional area of the roller cage can be made zero and the roller cage is prevented from extending to the elongated direction of the separation bar at the time of press-molding the contact surface, the contact surface can be formed at the roller cage by the mold-pressing so as not to degrade the accuracy of the size of the roller cage.
The press die used for fabricating the roller cage for the roller bearing according to the present invention includes a pressing die which press-molds the-contact surface contacting with the rolling surface of the roller at the upper surface side peripheral portion of the window hole for receiving the roller of the roller cage, and a backing die which receives the lower surface of the roller cage in a state that the lower surface side peripheral portion of the window hole is floated thereby to hold the cage so that the lower surface side peripheral portion of the window hole can be deformed to the pressing direction.
Preferably, the backing die includes a projection portion which protrudes from the general surface not contacting with the pressing die and contacts with the lower surface of the roller cage, and slanted surfaces each of which extends between the projection portion and the general surface and receives the lower surface side peripheral portion of the window hole expanding to the backing die side.
That is, according to the press die of the present invention, when both the contacting width of the projection portion of the backing die contacting with the lower surface of the separation bar of the roller cage and the slanted angle of the slanted surfaces are set suitably, the amount of the sectional area of the separation bar which is reduced when the pressing die presses the upper surface side peripheral portion of the window hole can be made equal to the amount of the sectional areas of the separation bar which is increased due to the expansion of the lower surface side peripheral portion of the window hole to the backing die side, and the roller cage can be prevented from being extended to the elongated direction of the separation bar.